1. Field of the Invention
The present invention relates to a method and a device for virtual concatenation transmission, and in particular to a method and a device for virtual concatenation transmission which multiplex low-speed frame traffics into a high-speed frame based on virtual concatenation.
In recent years, demands for various kinds of data communication lines have been growing in e.g. SONET/SDH optical transmission systems, as information services through the Internet or the like rapidly become widespread. In such data communication lines, it is required to treat data of various kinds/capacities as traffic. Specifically, in information services provided through the Internet in these several years, kinds of data treated are not only character information but also successively expanded to media such as voices, images, and moving images. It is assumed that data will be further varied in the future.
In order to accommodate to the data variety, it is required that a transmission system can efficiently and flexibly transmit multi-media data.
2. Description of the Related Art
FIG. 21 shows an STS-N (N=1, 3, 12, 48, 192, and 768) frame in a conventional SONET/SDH optical transmission system. This STS-N frame is formed of 9 rows×(90×N) columns bytes comprising an overhead (hereinafter, occasionally abbreviated as OH) of 9 rows×(3×N) columns bytes and a payload (Synchronous Payload Envelope: hereinafter, occasionally abbreviated as SPE) of 9 rows×(87×N) columns bytes.
The OH comprises A1 and A2 bytes for frame synchronization located at the first row and an AU pointer (Administrative Unit Pointer: hereinafter, occasionally abbreviated as PTR) composed of H1-H3 bytes located at the forth row, or the like.
FIG. 22 shows a low-speed STS-1 frame in case N=1 in the above-mentioned STS-N frame. This STS-1 frame is formed of 9 rows×90 columns comprising a TOH (Transport Overhead) of 9 rows×3 columns bytes including a single set of H1, H2, H3 bytes or the like, and an SPE of 9 rows×87 columns bytes. Accordingly, a bit rate of the STS-1 frame is 9×90×8 bits/125 μs=51.84 Mbps.
Furthermore, FIG. 22 shows a virtual container accommodated in the STS-1 frame. This virtual container comprises a Path Overhead (hereinafter, occasionally abbreviated as POH) of 9 rows×1 column bytes composed of J1, B3, C2 bytes or the like and a payload portion of 9 rows×86 columns bytes.
FIG. 23 shows an example of a path alarm detected based on the above-mentioned H1, H2, C2, B3 bytes or the like. The path alarm includes LOP (Loss of Pointer) and PAIS (Path Alarm Indication Signal) based on the H1 and H2 bytes, UNEQ (STS Path Unequipped), PLM (STS Payload Label Mismatch) and PDI (STS Payload Defect Indication) based on the C2 byte, and B3MAJ (B3 (CV-P; Code Violation-Path) Major Alarm), B3MIN (B3 (CV-P; Code Violation-Path) Minor Alarm) and the like based on the B3 byte.
In the same way as FIG. 22, when N is assumed to be 192 in the STS-N frame of FIG. 21, the frame is a high-speed STS-192 frame. This STS-192 frame is formed of 9 rows×(90×192) columns bytes comprising OH of 9 rows×(3×192) columns bytes including the AU pointer or the like further comprising 192 sets of H1, H2, and H3 bytes and SPE of 9 rows×(87×192) bytes. Accordingly, the bit rate of the STS-192 frame is 9×90×192 channels×8 bits/125 μs=9.95 Gbps.
FIG. 24 shows a transmission (multiplexing) order when 192 channels are transmitted by the STS-192 frame with the STS-1 being regarded as 1 channel. The STS-1×192 channels (CH1-CH192) are sequentially hierarchized into the STS-3, STS-12, STS-48, and STS-192 by byte interleave to be multiplexed.
In the conventional SONET/SDH optical transmission system (OC-N (N=1, 3, 12, 48, and 192)), for the transmission of data traffic having capacity corresponding to an STS-Mc (M=1, 2, . . . , and N), it has been required to secure a concatenation area of an STS-Lc (L=1, 3, 12, 48, and 192).
Furthermore, mapping of the STS-Lc into the OC-N can not be performed to arbitrary STS-1×L channels, but can be performed only to consecutive channels CHK, CH(K+1), . . . , and CH(K+L−1) (K=j*L+1; j=0, 1, 2, . . . , and N/L−1).
Accordingly, in spite of the existence of idle channels of more than L channels in the OC-N, mapping of the STS-Lc can not be performed in some cases, which leads to lack of systematic flexibility.
For this reason, manual operations by operators for systematically assigning data traffic to channels based on a prior estimation have been required.
Also, when a concatenation line is newly provided in response to an unexpected request, rearrangement of existing service lines has been required for securing the concatenation area in some cases.
FIGS. 25A-25D show a case where data traffic of 1.2 Gbps (STS-24: 24CH) are mapped into the STS-192 (OC-192) frame by the STS-48c concatenation. It is to be noted that although the STS-1 of CH1-CH192 is multiplexed into the STS-192 as shown in FIG. 24, the channels CH1-CH192 are supposed to sequentially multiplexed in FIGS. 25A-25D, in order to facilitate understanding.
FIG. 25A shows a present channel occupation state. The channels CH2, CH82, CH140, and CH159 are in an occupied state and the other channels are in an idle state.
In order to transmit 1.2 Gbps data traffic corresponding to 24 channels of FIG. 25D by concatenation, the capacity is short in the concatenation area of the STS-12c. Therefore, the concatenation area of the STS-48c, which is in an upper hierarchy than the STS-12c, has to be secured.
Therefore, in order to secure the area of the consecutive channels CH145-CH192 as the STS-48c concatenation area in FIG. 25B, an existing service channel CH159 is rearranged to the channel CH124. Then, as shown in FIG. 25C, the area of the channels CH145-CH192 is secured as the STS-48c concatenation area, and the 1.2 Gbps (STS-24: 24CH) data traffic are mapped into the STS-48c concatenation area.
For executing this, following problems arise: (1) Manual operation by operators is required for a systematic channel assignment; (2) When the 1.2 Gbps data are mapped and transmitted within the optical transmission system, the STS-48c of 2.4 Gbps is required to be assigned, and channels for 1.2 Gbps (≈2.4 Gbps-1.2 Gbps) are wasted; (3) Instantaneous interruption of existing service channel occurs concurrently with rearrangement of the channel CH159 to the channel CH124. Also, in the conventional virtual concatenation system, phase synchronization between virtual-concatenated channels is made at a terminal point to be treated as a bulk.
Since virtual slave channels independently generate a pointer action in this system, deviation between payload phases occurs during a transmission through a network. Accordingly, a memory circuit for absorbing the deviation is required. Also, the difference of pointer values between the virtual slave channels is prescribed due to a limitation of the memory capacity, which leads to constraints for constructing the optical transmission network.